Abstract
The flaking failure in rolling contact fatigue (RCF) results from crack initiation and propagation has been believed to originate from non-metallic inclusions located beneath the surface. With conventional microscopies, however, damage process in the internal region of materials could not be observed, then RCF crack initiation and propagation behaviours were observed by using synchrotron radiation computed laminography (SRCL) in the brightest synchrotron facility in Japan, and the effect of the inclusion orientation on the RCF property was examined. In our previous studies, crack initiation and propagation behaviours caused by extended MnS inclusions distributed in depth or transverse (width) direction was observed by the SRCL. In the present study, the fracture mechanism under RCF was discussed on specimens with MnS inclusions distributed in the rolling direction. As a result, vertical cracks were initiated on the surface, parallel to the ball-rolling direction in specimens. The crack propagation direction was then changed perpendicular to the rolling direction. Thereafter, similar with our previous studies, vertical cracks caused the horizontal cracks beneath the surface, when the vertical cracks reached to a critical length. The ratio of the vertical crack initiation life to the flaking life was higher than specimens with other inclusion orientation.
Highlights
Roller bearings are used in various machinery such as cars, air planes and electrical appliances
Shear-type cracks parallel to the rolling direction and surface were formed, while vertical cracks perpendicular to the rolling direction were first formed from stringer-shaped inclusions
4D observations of the formation and propagation of cracks in the rolling contact fatigue (RCF) tests were performed on a highstrength steel by combining a newly developed compact RCF testing machine with synchrotron radiation computed laminography (SRCL), and the crack propagation behavior and the fracture mechanism under RCF was discussed on specimens with MnS inclusions elongated in the rolling direction (L-Type)
Summary
Roller bearings are used in various machinery such as cars, air planes and electrical appliances. In order to improve bearing life, it is necessary to investigate the rolling contact fatigue (RCF) mechanism. Martin et al dealt with microstructural alterations, which develop with cyclic stressing under rolling contact, and attempted to define their nature and formation mechanisms [3]. Shear-type cracks parallel to the rolling direction and surface were formed, while vertical cracks perpendicular to the rolling direction were first formed from stringer-shaped inclusions. In this case, shear-type cracks were formed after the formation of the vertical cracks. Tsuchida and Tamura observed that horizontal cracks were formed from spherical inclusions, they considered that the crack initiation was controlled by the normal stress [9]
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